Bees and other pollinators use scents to track down fresh flowers. Air pollutants can weaken or even scramble those scents. Scientists had worried that this might make it harder for some pollinators to find a meal. And indeed, a new study concludes, in some cases it could quadruple the pollinators’ effort.
Many animals help pollinate plants. They do this by bringing grains of pollen from one plant’s male parts to the female parts of another plant. Species that do this include bees, butterflies, moths and beetles. But for many reasons, the pollinators available to help plants in this way have been declining. Scientists think that a loss of habitat — good places to live — could be one factor. Diseases, parasites and exposure to certain pesticides also may be playing some role.
Jose Fuentes points to air pollution as yet another possible factor. He’s an atmospheric scientist at Pennsylvania State University in University Park. In an earlier study, he showed that some air pollutants could weaken or destroy scents given off by flowers. If the pollinators can’t smell the blooms, they may have to bumble around longer searching for lunch.
Foraging for a meal leaves pollinators out in the open and at risk of becoming some other animal’s lunch. And any time spent hunting food is time away from their duties back home, such as protecting a hive or nest, explains T’ai Roulston. He is an insect biologist at the University of Virginia in Charlottesville. Roulston worked with Fuentes on the new study.
The team decided to probe how pollution might affect the lunch break bees would take from a hive. The group used a computer to model scent changes in response to various polluting chemicals in the air. Their data now indicate bees and other insects could take longer — much longer — to find and follow scents to a meal. The scientists have just shared their findings in the July 1 issue of Atmospheric Environment.
What the computer predicted
Flowering plants emit gases that perfume the air. The fragrant molecules disperse and create a scented plume. Like a game of hot and cold, pollinators use their antennae to follow the gradient, always looking for where the scent strengthens. A strong scent means they are closing in on a bloom. A weaker scent means they’re drifting off course.
The researchers focused on five representative floral scent molecules. One molecule they looked at, for example, is called beta-myrcene (BAY-tuh MER-seen). A number of blooms emit this chemical into the air. Among them: snapdragons, purple coneflower, parsley, hops and certain citrus plants. Normally, this gas can travel some 800 meters (0.5 miles) from its flower source. But in polluted air, this same molecule could travel only half as far. Changes to beta-myrcene and other scent molecules as they interacted with the pollutants meant that insects would have to spend longer in search of a meal.
About 50 percent of foraging insects can sniff out a particular scented plume in 15 minutes if the air was clean. But the same insects could take an hour, the computer predicts, to find the scent plume when air is moderately polluted with ozone. Ozone is one of the primary irritants in urban smog. And the level of ozone considered here would be typical for a major U.S. city on a hot summer day, notes Fuentes.
These findings give scientists clues about what may be going on in nature, says James Blande. He is a chemical ecologist at the University of Eastern Finland in northern Europe. He wasn’t involved with this research. Still, he says, “it’s important to test these assumptions in real world experiments before drawing any firm conclusions.”
But air pollution might do more than just weaken scent plumes. Chemical reactions between air pollutants and plumes may transform the blooms’ fragrances, creating new scents. And these scents may be unrecognizable to pollinators.
That’s certainly Fuentes’ concern. So, he says his next research project will be to look at how insects deal with any new floral scent. “It is possible that some insects will evolve ways to detect and use these new molecules to find food,” he says.
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atmospheric science A field of meteorology that is related to climate science and pollution impacts. People who work in this field, called atmospheric scientists, use computers and math to model the properties of Earth's atmosphere that drive weather, climate and the movement of gases and pollutants through the air.
chemical ecology The study of how plants and animals use chemicals and chemical signals in their interactions with each other and their environment. Scientists who work in this field are called chemical ecologists.
chemical reaction A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).
entomology The scientific study of insects. One who does this is an entomologist.
evolution (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the conditions in which it developed.
forage To search for something, especially food. It’s also a term for the food eaten by grazing animals, such as cattle and horses.
gradient From the word “grade,” it describes the incline, slope or degree of increase in some measure (such as temperature, pressure or even color) that develops as one moves in time, position or along some scale.
habitat The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
ozone A colorless gas that forms high in the atmosphere and at ground level. When it forms at Earth’s surface, ozone is a pollutant that irritates eyes and lungs. It is also a major ingredient of smog.
parasite An organism that gets benefits from another species, called a host, but doesn’t provide it any benefits. Classic examples of parasites include ticks, fleas and tapeworms.
pesticide A chemical or mix of compounds used to kill insects, rodents or other organisms harmful to cultivated plants, pet or livestock, or unwanted organisms that infest homes, offices, farm buildings and other protected structures.
plume (in environmental sciences) The movement of some gas or liquid, under the direction of gravity, winds or currents. It may be in air, soil or water. It gets its name from the fact that it tends to be long and relatively thin, shaped like a large feather. (in geology) Fluids (air, water or magma typically) that move, largely intact, in a feather-like shape over long distances.
pollinator Something that carries pollen, a plant’s male reproductive cells, to the female parts of a flower, allowing fertilization. Many pollinators are insects such as bees.
pollutant A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.
predator A creature that preys on other animals for most or all of its food.
smog A kind of pollution that develops when chemicals react in the air. The word comes from a blend of “smoke” and “fog,” and was coined to describe pollution from burning fossil fuels on cold, damp days. Another kind of smog, which usually looks brown, develops when pollutants from cars react with sunlight in the atmosphere on hot days.